Electric wave repeater for multiplex transmissions



July 7, 192a 1,544,943

. 5. 0. SCRIVEN, 4

EL ECTBIC WAVE REPEATER FOR MULTIPLEX TRANSMISSIONS Original Filed Sept; 27.. 1919 //1 1 01 for.

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' 2y ga 4 y- Patented July 7, 1925.

UNITED STATES PATENT OFFICE.

EDWARD O. scRIvEN, or NEW'YOR N. Y., AssIGNOR To WESTERN ELECTRIC COM? PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OE NEW YORK.

ELECTRIC WAVE REPEATER FOR MULTIPLEX TRANSMISSIONS.

Application filed September 27, 1919, Serial No. 326,904. Renewed April 29, 1925.

To all'whomit may concern. 4'

, Be it known that I, EDWARD O. SCRIVE-N, a citizen of the United States, rcsiding at New York, in the county of New York, State Of New York, have invented certain new and useful Improvements in Electric WVave Repeaters for Multiplex Transmissions, of which the following is a full, clear, concise, and exact description.

This invent-ion relates to electric wave repeaters, wherein are employed electric discharge tubes or equivalent dcvices, and multiplex systems employing such repeaters.

The general Object of the invention isto improve upon repeaters and particularly repeaters for multiplex systems. v

' In the patent of Colpitts 1,128,292 granted February 16, 1915, there is shown a pair of vacuum tubes connected in opposition or push-pull relation, as an electric wave amplifier. Push-pull connection of vacuum tubes will herein indicate the relationship where the input or control electrodes are connected to an inputline so that one is made positive whenthe other is made negative and the output circuits are connected to an output line so that increase of current in one output circuit has a similar effect upon the output line as a simultaneous decrease of current in the other output circuit. It has been found that by utilizing suitable impedance elements in such amplifying circuits that the repeating powers of the apparatus are improved. Previously it has been customary in selecting vacuum tubes for such push-pull amplifying circuits to secure tubes having as nearly identical electrical characteristics as possible, because if the tubes did not have, identical characteristics a certain amount of distortion or imperfection of operation resulted. Likewise, imperfect operation resulted from unbalance; that is,

dissimilarity of the correspondin branches v 7 of the divided circuit associate with the vacuum tubes. In practice it is very-difiicult to secure vacuum tubes which arev identical in all respects. Even if two specimens of a lot were identical in characteristics much time would be consumed in exhaustive tests to select that particular pair, and moreover it is impractical to exactly balance two sides of the divided circuit. By the use of th1s invention the results secured with slightly unbalanced circuits or tubes are very much improved. In a system operating in accordance with this invention it is desirable that for the particular frequency or frequencies to be repeated an increase of space or anode-cathode current through one tube will cause anequal andsimultaneous decrease of current through the other tube.

The impedance element or elements to be added are designed with this end in view.

A desirable push-pull circuit for the tant novel features based on the discovery that, if amplifyingor repeating devicesas herein described are used to repeat the Waves in a multiplex system wherein electrical waves due to ordinary speech currents and one or more modulated high frequency waves 'are simultaneously transmitted, the modification of the Waves of any one frequency by the Waves of any of the other frequencies, is prevented. Thus by Way of example, it is' possible to repeat simulta neously one ordinary telephone conversation, a control current of 5,000 cycles, and modulated waves' of 10,000, 15,000 and 20,000 cycles respectively, without any of the waves being modulated or affected by any of the other Waves, This invention originated in an attempt to use repeaters as herein described as carrier eliminating modulators or detectors, with the resulting discovtection resulted. The use of the high impedance choke coils 8 and 14 seems to pre- 55 vent modulation or detection. From this discovery arose the idea of utilizing this sort of repeater in multiplex systems to avoid theprevious difficulties ofoperation resulting from. the modulation of waves of one freq y ll accordance with waves of other what complicated hence no attempt is made herein to outline any elaborate or exact theory as to the operation of the described ar- .rangements in repeating without modula- 'tion waves of several frequencies or bands of frequencies other than to say that the result seems to depend upon the fact that the systems act in a manner which would be expected if the input-output characteristic was linear over the whole working range.

The invention is explained in connection with the accompanying drawings, wherein Fig. 1 represents the preferred arrangement; Fig. 2 is a modification wherein a double vacuum tube is used; and Fig. 3 is another modification in which no input or output transformer is used. Corresponding reference characters indicate corresponding parts of the dilferent figures and the description of one element is equally applica ble to elements in other figures having the same characters applied thereto.

A, A indicate input terminals and B, B indicate output terminals. Any suitable source of current variations to be repeated or amplified may be connected to the terminals A, A and any suitable receiving circuit or'device to the terminals B, B. For the purpose of illustrating the invention as used m a multiplex transmission system, the sources :0, w, and m" are connected to terminals A by a connecting circuit or line of 'any suitable length or nature. a: may represent a source 'of voice or sound currents or waves, a" a source of waves of a base fre- .quency of 10,000 cycles modulated in accordance with speech, and m" a source of simllarly modulated waves of a base frequency of 15,000 cycles. Each source 41:, w, and a2" 'W'Ill be of such nature .orwill be in circuit with such apparatus as will prevent the short-circuiting therethrough of the wavesfrom the other sources The invention is not limited to any particular number of sources of waves, kinds of waves or manner of impressing them upon the line.-

Primaries 1', 1 of the input transformers are connected between terminals A, A and secondaries 2, 2 are respectively coupled to the primaries -1, 1 and connected between the control grids and cathodes 6 ofthe tubes 3 respectively. When incoming waves make one grid positive the other grid is made correspondingly negative, each with respect to its associated cathode. If desired, the

1, 1 and 2, 2 may be combined into a single primary 1' and secondary 2' as in dicated in Fig. 2. In this case the filament lead will be connected to the middle point of the secondary. Referring again to Fi 1, the output or anode-cathode circuits 0 the tubes 3 are in 0% to terminals and pass from plates osite relation with respect 4 through the coils 5 to the filamentary cathodes 6, through the common branch 7. The common branch 7 contains a highly inductive impedance element 8 which is designed to olfer a very high.

7 will be connected to the-midpoint of the primary. The usual sources of electrical energy 10, 11, and 12 are provided to properly polarize the grid electrodes, to heat the cathode, and furnish anode-cathode current, respectively.

In Fig. 2

vacuum tube devices are combined .into a single evacuated vessel 3'. The filament 6 serves as a source of electrons for an electron stream to each of the anodes 4:. Since such double vacuum tubes are described in prior publications and are merely mentioned here to illustrate their possible use in connection with the present invention, lio further dethe filamentary cathodes 6 are replaced by single cathode 6, and the twoscription of the tube itself will be given. A

single input transformer having-a primary 1" and a secondary 2' and a single output transformer having primary 5 and second ary 9' are used. The transformer arrangements of Figs. 1 and 2 are mutually interchangeable.

In F ig. B'the input voltages for the two tubes are derived from resistances 13 which are across the input terminals A, A, of the apparatus. The resistances 13 serve as asubstitute for the input transformers of Fig. 1. Each of the anode-cathode direct current circuits of the tubes contains a coil 14 which 'is designed to offer a very high impedance to currents of the frequency or frequencies being repeated. Coilsl' ttogether function to maintain the sum of the anode-cathode currents of the two tubes constant. Condensers 15 and 16 may be used to isolate the repeating apparatus from the effects of direct current voltage sources attached to the terminals A, A or B, B and also prevent the flow of any continuous current through the respective conductors in which the tubes are not equal. Condensers 15 and i 16 are not essential but if used are preferab y of large capacity so as'to offer low-im' impedance of that particular tube.

pedance to alternating currents passing therethrough. A resistance 17 may be shunted across the output terminals B, B in I case it is desired to reduce the output impedance. The output circuit of an arrangement such as shown in Fig. 3 includes all the elements connected between the anode and the cathode, but may be regarded as having a direct current output circuit or path and an alternating or effective outputcircuit or path.

In operation, when the grid or control electrode of one tube becomes more negative with respect to its associated cathode, and thus increases the impedance of one tube, the grid of the other tube simultaneously becomes more positive, and thus decreases the Even though the characteristics of the tubes are not identical, the action of the impedances 8 or 14 will tend to cause the increase of current through one tube to be equal to the decrease through the other. Likewise, distortion due to the unbalance of the respective branches of the divided circuits will tend to be reduced. For example, if the mutual inductance between one pair of coils-5, 9 in Fig. 1 is greater than the mutual inductance of the other pair of coils 5, 9, this will correspondingly effect the induced potential between the terminals B, B which is proportional at any instant to the sum of the rates of change ofcurrent through coils 5, 5. multiplied by their respective mutual inductances with coils 9, 9. Any change of current in one of the coils 5 is accompanied by an equal change in the other coil because the coil 8 powerfully tends to maintain a constant current through itself, hence the effect induced in the output line by a one-half cycle of asymmetrical input current tends to be identical in magnitude with the effect produced-by a succeeding half cycle. The effective alternating current output circuit path, in case of Figs. 1 and 2, is through the primaries 5 or 5, while in the case of Fig. 3, it is through any line or apparatus connected to the terminals B. The direct current paths between the anodes and the cathodes of the tubes 3 are through the coil 8 in Figs. 1 and 2, and through the coils 14 in Fig. 3. These paths may be partly through the conductors comprising the effective alternating current output circuit path, or they may be independent of that part thereof which is external to the vacuum tube. There will, therefore, result in any suitable circuit attached to the terminals B, B, current waves of the same nature and frequency as are simultaneously applied from the sources at, m and 02". None of thesewaves will be modulated in accordance with any of the other waves and each may be separated from the others by suitable filters, selective cir-' cuits, or other means, and used to'reproduce the signal or conversation individual to that wave, or otherwise applied for useful purposes in any of several ways known in the art.

Claims directed'broadly to the use of a common repeater for simultaneously repeating the waves employed by a plurality of carrier transmission channels are not included in this application, since this broad subject matter is the invention of another and is being claimed in an application of Burton W. Kendall Serial No. 334,681, filed October 31, 1919. Also, certain specific aspects of the subjectmatter disclosed herein and involving the use of a pair of impedances, as shown in Fig. 3, are claimed in a copending ap lication of Robert O. Mathes Serial No. 33 ,565, filed November 12, 1919.

The novel features believed to be inherent in the invention are defined in the following claims.

WVhat is claimed is;

1. In combination, a plurality of separate sources of waves of respectively different frequency, an electric wave repeating apparatus comprising divided input and dividedv output circuits, means for simulta neously impressing waves from said sources upon the input circuit, means for producing two ionized streams, said streams being oppositely included in said output circuit, two control elements for controlling said ionized streams respectively connected to said input circuit, a common branch for said output circuits, and an inductance of large value included in the output circuit effective at -the frequencies to be repeated to offer high impedance to waves passing through said common branch.

2. In combination, a plurality of separate sources of waves of respectively different frequency, an electric wave repeating ap-.

paratus comprising divided input and divided output circuits, means for simultaneously impressing waves from said sources upon said input circuits, means for producing an ionized stream included in each division of said output circuit, and control elements, one in each division of said input circuit, for controlling said ionized streams respectively, said output circuits having a common portion and an inductive impedance in said portion of such value as to substantially prohibit the passage therethrough of currents of the frequencies to be repeated.

3. In a multiplex wave repeating system, a plurality of sources of signaling waves of different frequencies to be repeated, a repeater therefor comprising two space discharge devices each comprising a grid, an anode and an electron emitting cathode, grid-cathode and anode-cathode circuits for each of said devices, said anode-cathode circuits each being coupled to an output line and having a portion in common, said common portion lncludin an inductance element of high inductive value 'in circuit whereby said common portion is caused to be of hlgh inductive reactance at all the frequencies of waves to be repeated, and an incoming line. for supplying waves of the va' rious signaling frequencies to said gridcathode circuits.

In witness whereof, I hereunto subscribe 10 my name this 25th day of September, A. D. 1919. V

EDWARD O. SCRIVEN. 

